1. Field of the Invention
This invention relates to a fluid dynamic pressure bearing device that may be used in a motor, particularly a small, thin spindle motor. The fluid dynamic pressure bearing device is excellent in bearing rigidity and rotation precision and also excellent in suppression of lubricant leakage and splashing due to external vibration or shock applied during motor stopping and rotation, for example. The fluid dynamic pressure bearing device can also reliably engage with a rotor member. The invention also relates to a spindle motor and a recording disk drive device provided with the fluid dynamic pressure bearing device.
2. Description of Related Art
Recently, hard disk drives have been made smaller, thinner, larger in hard disk storage capacity, and faster. Meanwhile, devices such as computers or the like in which hard disk drives are mounted have been made smaller and lighter, and application of the hard disk drives to portable devices has become widespread. In the case of portable devices, vibration and shock due to carrying frequently occur. For example, there are many chances for vibration and shock to occur during motor rotation while the portable devices are being used during transportation on trains, planes, vehicles, etc. There is a strong demand for rotation precision and other reliability assurances to help avoid adverse effects from the vibration and shock that can occur in these situations. This invention responds to that demand.
Japanese Laid-Open Patent Application 2002-155940A discloses a fluid dynamic pressure bearing device intended to solve the problem of torque increase and the problem of lubricant liquid leaking to the outside, which occur as a flange diameter of a shaft becomes large, and which are obstacles to designing smaller fluid dynamic pressure bearings.
As shown in FIGS. 1 and 2 of the above-mentioned application (FIGS. 10 and 11 of this application), this fluid dynamic pressure bearing device is provided with a housing 01 and a shaft 03 that is rotated within a through-hole 02 of the housing 01. Lubricant 06 is filled in a gap between the housing 01 and the shaft 03. A flange 04 of the shaft 03 is engaged with an annular concave portion 05 on an inner surface of the housing 01. Thrust dynamic pressure generating portions B1, B2 are formed between upper and lower surfaces 04a, 04b of the flange 04 and the annular concave portion 05. Furthermore, to solve the above-mentioned problems, communication paths 011 are formed that extend from the through-hole 02 side of the housing 01 to the outer surface 05c of the annular concave portion 05, and open to the through-hole 02 and to the outer surface 05c. These communication paths 011 are formed in the portion of housing 01 that is on the side of the upper surface 04a side of the flange 04.
FIG. 4 of the above-mentioned application (FIG. 12 of this application) shows another related structure. When a top surface 044a of a flange 044 of a shaft 043 facing a thrust dynamic pressure generating portion B1 is floatingly rotated, or approaches an upper side inner surface (ceiling surface) 045a of an annular concave portion 045 formed in an inner surface of a through-hole 042 of a housing 041 due to vibration and/or shock, lubricant on the thrust dynamic pressure generating portion B1 side is compressed, and a negative pressure is created in the lubricant on the thrust dynamic pressure generating portion B2 side, which is on the opposite side of the flange 044 from the thrust dynamic pressure generating portion B1. Therefore, B1 side lubricant must be promptly moved to the B2 side. In order to perform this movement promptly, through-holes 051 that communicate between the B1 side and the B2 side are formed parallel to the shaft.
However, in order to form the shaft-direction through-holes 051 shown in FIG. 12, the external diameter dimension of the flange 044 needs to be enlarged to provide enough space for the through-holes. When the external diameter dimension is enlarged, there is a problem in that the torque increases. To suppress the torque increase, the invention described in Japanese Laid-Open Patent Application 2002-155940A discloses that instead of the through-holes 051, communication paths 011 are formed in the housing 01 portion on the upper surface 04a side of the flange 04, as shown in FIG. 2 (FIG. 11 of this application). These communication paths 011 pass from the through-hole 02 side of the housing 01 to the bottom surface 05c of the annular concave portion 05, and are opened to the through-hole 02 and the bottom surface 05c. Furthermore, each communication path 011 is constituted by a diameter-direction hole 011a and a cut portion 011b that intersects the diameter-direction hole 011a and is opened to the bottom surface 05c of the annular concave portion 05.
An object of the fluid dynamic pressure bearing device of the above-mentioned application is to eliminate the shaft-direction through-holes 051 (see FIG. 12 of this application) and suppress the increase of the external diameter dimension of the flange 04 of the shaft 03, and thereby suppress torque increase. A solution to the problem is to form communication paths 011 in the housing 01 portion opposite to the flange upper surface 04a. As a secondary effect of forming these communication paths 011, there is generated an operation effect of stopping the lubricant in the cut portions 011b of the communication paths 011. Thrust dynamic pressure generating grooves are directly formed in the flange top surface 04a. Opposite to the thrust dynamic pressure generating grooves, a surface that directly receives a generated thrust dynamic pressure force is arranged on the housing 01 portion. This surface is an inner surface 05a, which makes a ceiling surface of the annular concave portion 05. The communication paths 011 are formed at a predetermined depth from the inner surface 05a, pointing in a diameter direction.
Furthermore, in the fluid dynamic pressure bearing device of the above-mentioned application, when the gap at the thrust dynamic pressure generating portion B1 or B2 reduces, lubricant is smoothly circulated via the communication paths 011 formed in the housing 01. Therefore, lubricant leakage from an outside opening portion 07 of the through-hole 02 of the housing 01 can be suppressed.